The present invention relates to data communication networks, and more particularly to systems and methods for discovering and verifying links between nodes.
Internet traffic is typically forwarded from a source to a destination through a series of nodes connected by links. The nodes represent network devices such as routers, switches, etc. The links are physical media such as optical fiber, twisted pair, etc. and often connect a pair of nodes. Various protocols that control the forwarding of packets through a network depend on each node having a correct understanding of the links available to its immediate neighbors.
Typically, discovery and/or verification of a link between two nodes is accomplished by an exchange of packets over the link. As will now be explained, however, this exchange of packets is problematic for an important new class of network devices.
To accommodate increasing volumes of network traffic, the Internet is relying more and more on the vast bandwidth of optical fiber media. Routing and switching operations, however, have largely remained in the electrical domain. The need to convert optical signals to electrical fort and then perform switching and/or routing computations on the electrical signals has become a bottleneck for optical networks. In order to remove this bottleneck, all-optical cross-connects (OXCs) have emerged as an important building block for optical networks. In an OXC, optical inputs and outputs are coupled to one another through a switching matrix without intermediate conversion to an electrical signal. Since the optical signals pass through untouched, OXCs do not incorporate expensive hardware either for conversion to electrical form and reconversion to optical form, or for processing packets in accordance with a protocol. This results in enormous savings in cost and extremely high throughput. Another advantage of the OXC is that it requires no special adaptation to the protocol or data rate of the data carried by the switched optical signals.
To best integrate OXCs into the Internet, it is desirable to discover and verify links to and from them. However, if an OXC is to exchange packets with its neighbors for the purpose of link discovery and verification according to conventional techniques, it will have to incorporate line termination capability, i.e., the ability to generate and interpret packets in accordance with a protocol used by a neighbor. Supporting this capability will require that a line termination unit (LTU) capable of generating and interpreting packets according to the relevant protocol be incorporated within the OXC. To maximize the number of protocols which use an OXC, it will be desirable to incorporate a separate line termination unit (LTU) for each anticipated protocol that might be terminated by a neighboring node. Each LTU would incorporate the electrical to optical and the optical to electrical conversion circuitry as well as high speed packet processing that would otherwise be made unnecessary by use of the OXC.
Furthermore, when a particular OXC switch port is having its neighbor connectivity verified, that port must be switched to another port connected to the correct LTU so that the appropriate packets may be exchanged. Thus, each LTU that is needed consumes a port and also a significant percentage of the available switching resources. It becomes clear then that current link discovery and verification techniques are expensive to apply to optical switching equipment that is not otherwise capable of originating and/or interpreting packets via optical links.
Another type of device that is finding increasing application on the Internet is the dense wave division multiplexer (DWDM) that multiplexes signals from several incoming fibers onto multiple wavelengths on the same fiber and demultiplexes multiple wavelength components carried by the same fiber onto separate filers. By allowing the combining of numerous signals on the same fiber, DWDMs greatly expand the transmission capacity without increasing the data rate of individual optical signals, thus simplifying the electronics needed to generate and interpret the payload data streams modulated onto the optical signals. DWDMs are also preferably insensitive to protocol and data rate.
DWDMs, depending on the application, may or may not incorporate hardware to convert optical signals to electrical signals and vice versa. However, DWDM equipment does not typically include the capability to terminate packets that are being carried by optical signals. As with OXCs, this represents an obstacle to current link discovery and verification techniques.
What is needed are systems and methods for link discovery and verification that minimize the needed line termination resources and are thus suitable for implementation on devices that do not otherwise provide extensive line termination capabilities such as OXCs and DWDMs.